Fluid heat exchange apparatus



Aug. 6, 1940. D. s. JAcoBus FLUID HEAT EXCHANGE APPARATUS Original FiledNov. 20, 1934 INVENTOR.

Patented ug. 6, 1.94()y PATENT OFFICE 2,209,974A A FLUID HEAT EXCHANGEAPPARATUS David S. Jacobus, Montclair, N. J., assignor to The Babcock &Wilcox Company,

Newark,

N. J., a corporation of New Jersey Original application November 20,1934, Serial No. 753,828. Divided and this application October 16, 1937,Serial No. 169,440

5 Claims.

This invention is predicated upon improvements in metallic `tubularstructures, and-.it is exemplified herein by tubular connectionsemployed in fluid heat exchange apparatus.

When, in such apparatus, a fiuid at one temperature passes through tubesto a, metallic vessel at a higher temperature, experience has shown thatthe consequent differential metal expansions soon cause defects in theconnections between the tubes and the metal of the vessel. This isespecially true of economizer tubes connected to the drums of steamboilers operating at high fluid pressures.

It is an object of the invention to overcome this disadvantage.

A further object is to provide a Stirling boiler with an integraleconomizer the tubes of which are joined to a feed-water drum inaccordance with the teachings of this invention.

Other objects will appear from consideration of the followingYdescription ofthe Stirling water tube steam boiler shown in theaccompanying drawing, in which:

Figs. 1-5 inclusive are detail sections indicating different steps of amethod which may be employed in practicing the invention.

Fig. 6 is a vertical section through a boiler drum having tubesconnected thereto.

Fig. 7 is a section showing a tubular drum connection.

Fig. 8 is a view in the nature of a vertical section, showing a Stirlingboiler having an integral economizer.

Figure 9 is a sectional view.

The drawing discloses a Stirling boiler including the mud drum IIJ andthe upper steam and water drums l2, I4 and I6, the first of which isprovided with a steam off-take I'I. The latter drums are connected tothe mud drum by separate banks of steam generating tubes I8, 20 and 22,exposed 1n separate gas passes to furnace gases from the combustionchamber 24.

Feed water is supplied from any suitable source to the economizer drum'26 which is connected to the rear drum I6 bythe economizer tubes 28located in the last gas pass of the boiler. Although the temperature ofthe feed water is raised during its movement through these tubes it maybe at a. temperature much less than the temperature of the drum I6 whenit enters the latter. The tubes 28 therefore tend to contract relativeto the metal of that drum, causing a loosening of the tubes when theyare directly expanded into the drum. Furthermore, this undesirablecondition is aggravated by the continued supply of low temperature freshfeed water to the drum 26 and the continued circulation through the drumI6 of water which has been heated to a higher temperature by the tubes22 in the hottest gas pass. Such circulation takes place through thedruml I0 which directly connects thebanks of tubes I8 5 and 22.

When it is considered that many boilers of the type shown operate atfluid pressures in excess of 1000 lb. per sq. inch it will be readilyappreciated that any loosening of the tubes 28 in their seats in 10 thedrum I6 isapt to be a matter of no small moment. As a matter of fact,experience has shown that such results are grave disadvantages inboilers operating at much lower pressures. This is particularly truewhen the boilers are operated l5 at 300 to 500% ratings. The water levelin the drum I6 is apt to be below the upper ends of some of the tubes28. The connections of these tubes with the drum are then apt to becomeloosened so that steam leaks develop. It finally becomes 20 necessary totake the boiler oi the line for repairs, and if the tubes are merelyre-expanded into the drum, the same cycle is repeated. To avoid thisexcessive outage the economizer tubes are connected to the drum I6 inthe `manner described 25 given thickness of drum shell. In constructionsother than the Stirling boiler shown it is sometimes preferable torefrain from swaging down the ends of the economizer tubes where theyare connected to the steam and water drum. 40 As the next step in theillustrative procedure a sleeve 36 is telescoped upon the swaged end ofthe tube. When this sleeve is of the internal diameter shown it tstightly upon the ribsl 32 and 34 and is heldv in position thereby,spaced from the exterior surface of the tube. It is preferably formed ofsome self-supporting material, and, under different embodiments of theinvention the material may be paper, or a metal having a low 50 fusingtemperature. Low fusing point alloys may be used in some instances, andin others, a cellular heat insulating material. Tin and leadare examplesof metals which maybe used.

In the illustrative method, a tubular metallic 5 ferrule 40, preferablyof the same material as the tube, is tightly telescoped over the sleeve36. This may be done in some cases before the sleeve is placed in theposition shown in Fig. 3, but the particular sequence of these actsdepends upon the sequence of the remaining method steps, as well as uponthe materials used.

The sleeve 36 and the ferrule d0 both terminate coincidentally with thetube to facilitate the completion of the circumferential weld 42 whichforms a fluid tight connection between the tube and the ferrule but theinvention also contemplates the extension of the tube beyond the ferrulein some cases. The tube is now ready to be held within a. tube seat inthe drum I6 while an expander is operated within the tube to form arigid and uid tight drum connection. When the circumferential grooves 43and 44 are formed as parts of the tube seat, the expanding operationwill cause some of the metal of the ferrule to occupy the grooves tolock the ferrule more securely to the drum. Fig. 7 shows the grooves tobe entirely lled with such metal. The expanding operation may alsoresult in such a belling of the end of the tubes as indicated at 46 inFig. '7. This further locks the ferrule to the drum and tends to preventany endwise movement of the ferrule.

In some embodiments of the invention the ferrule 4I] may be separatelyexpanded against the tube seats, and the tubes thereafter co-axiallyplaced within and spaced from the ferrules so that the circumferentialwelds may then be completed. In these cases the ferrules may beadditionally welded directly to the drum metal, and this welding as wellas the expanding of the ferrules may be clone in the shop where the drumis manufactured. This promotes economy of manufacture by reducingerection costs.

When the boiler is put into operation after a heat convertible materialsuch as paper is used between the ferrule and the tube, the paper or thecompound formed on heating the paper acts to insulate the main body ofthe ferrule from the tube. When tin, lead, or some low fusing pointalloy is used as the sleeve, the latter melts when the boiler is placedin operation, leaving an annular space between the ferrule and thesleeve.

In some embodiments of the invention the ribs 32 and 34 may not beemployed. The sleeve may fit the tube tightly throughout its length.Such an arrangement of elements is indicated in Fig. 9 of the drawing,wherein the ferrule 48 may be expanded into the drum in the shop and thetube thereafter inserted and Welded to the inner end of the ferrule inthe field. With this construction there is an annular space between thetube and the ferrule.

The construction may be used to advantage for connecting alloy steelsuperheater tubes to the outlet header of a superheater when the headeris made of plain carbon steel. In such a case expanding the alloy steeltubes directly into the outlet header may result in leakage in ahydrostatic test of the superheater such as is usually made during ashutdown period after the superheater has been in service. Thecoefficient of expansion and contraction of the alloy steel on changingthe temperature is greater than in plain carbon steel and, on coolingdown the superheater after it has been in operation, the alloy steeltubes may leak where they are expanded into the carbon steel headers. Byemploying ferrules of plain carbon steel around the ends of the alloysteel superheater tubes arranged in the Way shown and described andextending the ferrules and tubes a suflcient distance into the headerthe difference in the expansion of the tubes and the ferrules will notcause the ends of the plain steel ferrules to become loose where theyare expanded into the header as these ferrules will have the samecoefficient of expansion as the header. This will overcome the tendencyto leak on account of a difference in the coefficients of expansion. Ifdesired, the ferrules may be welded to the header in which case it isadvantageous to have the same coefficient of expansion in the ferrulesas in the header. By Welding the ferrules to the header on the outsideof the header the stresses due to the expansion of the tubes and theferrules would be distributed along the lengths of the ferrules therebyavoiding a concentration of stress due to the reinforcing action of thewelding. The ferrules may be made of comparatively thin wall sectionbecause the tube ends would prevent them from collapsing.

What is claimed is:

1. In uid heat exchange apparatus, a thick walled pressure vessel in thenature of a drum or header, tubes of much less Wall thicknesscommunicating with the interior of the vessel and adapted in practice toconduct a liquid at lower temperature to the liquid supply in thevessel, metallic ferrules externally telescoped upon the ends of thetubes and spaced therefrom, a ller interposed between each ferrule andits tube, and circumferential welds joining the inner ends of the tubesand the inner ends of the ferrules; each filler cooperating with aferrule and a tube to maintain them in predetermined spaced relationshipwhile the assembly is being expanded to form a pressure tight jointbetween the ferrule and the metal of the drum.

2. In fluid heat exchange apparatus, a thick walled pressure vessel inthe nature of a drum or header, tubes of such less wall thicknesscommunicating with the interior of the vessel and adapted in practice toconduct a liquid at lower temperature to the liquid supply in thevessel, metallic ferrules externally telescoped upon the ends of thetubes and spaced therefrom, a ller interposed between each ferrule andits tube, the filler being formed of combustible material, andcircumferential welds joining the inner ends of the tubes and the innerends of the ferrules; each ller cooperating with a ferrule and a tube tomaintain them in predetermined spaced relatlon` ship while the assemblyis being expanded to form a pressure tight joint between the ferrule andthe pressure vessel.

3. In tubular connections between a steam and water drum and tubes.through which water is adapted to enter the drum at a temperature lowerthan that of the body of fluid within the drum, the drum being formedwith openings providing tube seats, the tubes having reduced endsextending a substantial distance into the interior of the drum, sleevesor ferrules externally telescoping the tubes and circumfcrentiallyinsulated therefrom, the ferrules extending similar distances into theinterior of the drum, and circumferential welds formed at the inner endsof the tubes and ferrules while the latter are maintained incircumferentially spaced relationship to the tubes, the ferrules and thetubes being simultaneously expanded into the tube seats.

4. In fluid heat exchange apparatus, a thick walled pressure vessel inthe nature of a drum or,

header, tubes of much less wall thickness communicating with theinterior of the vessel and 75 adapted inpractice to conduct a liquid atlower temperature to the liquid supply in the vessel, metallic ferrulesexternally telescoped upon the ends of the tubes and spaced therefrom, a1111er of a low fusing point metal interposed between each ferrule andits tube, and circumferential welds joining the inner ndsof the tubesand the v inner ends of the ferrules; each ller cooperating with aferrule and a tube to maintain them in predetermined spaced relationshipwhile the assembly is being expanded to form a pressure-tight jointbetween the ferrule and the pressure vessel.

5. In fluid heat exchange apparatus, a thick walled pressure vessel inthe nature of a drum or header, tubes of much less wall thicknesscommunicating with the interior of the vessel and adapted in practice toconduct a liquid at lower temperature to the liquid supply' in thevessel,.

the pressure vessel ends of the tubes having preformed circumferentialribs, metallic ferrules externally telescoped upon the ribbed ends ofthe tubes and spaces therefrom, a ller interposed between each ferruleand its tube, and circumferential welds joining the inner ends of thetubes and the inner ends of the ferrules; each illler cooperating with aferrule and a. tube to maintain them in predetermined spacedrelationship while the assembly is being expanded to form a pressuretight joint between the ferrule and the pressure vessel.

, DAVID S. JACOBUS.

